1. Field of the Invention
The present invention relates to a method and an apparatus for measuring a surface profile of an object.
2. Description of the Related Art
A surface profiler with an optical probe and a scanning system is used for measurement of a surface profile of an object.
An optical probe system 1100 as an optical surface profiler is illustrated in FIG. 1. The optical probe system executes a measurement called “confocal method” using a focusing spot. The laser beam emitted from a laser diode 1000 is collimated by a collimator lens 1001, and focused onto an object surface 1050 by a focusing lens 1005 via a Polarization Beam Splitter (PBS) 1002, a Quarter Wave Plate (QWP) 1003, and a focus shift device 1004. The reflected light from the object surface 1050 is focused by an imaging lens 1006 via the PBS 1002. When a pinhole board 1007 having a pinhole is conjugate to the object surface 1050, intensity detected by a detector 1008 may become a maximum. Changing the focal length using the focus shift device 1004, a length L is calculated by the focal length which has maximum intensity on the detector 1008. To obtain the surface profile, the optical probe system 1100 should scan the surface of the object 1050.
With the confocal method described above, a pitch of current diffractive optics such as diffractive grating and diffractive lens becomes less than 10 microns. The lateral resolution of this method is limited by the focused spot size, and typical size of a focused spot to be used for optical probe is approximately 1 micron. Therefore, the measurement results of surface profile near an edge (step) becomes inaccurate.
Accordingly, there is a need for a method for measuring a surface profile of an object which can more accurately obtain a measurement result of a surface profile near an edge.